This invention relates to a current-sensing circuit for sensing an output current of a power semiconductor arrangement, which comprises a semiconductor body having a first and a second current-carrying section, each section containing at least one basic semiconductor element. The first current-carrying section is arranged to carry a significantly higher current than the second current-carrying section and the first and second current-carrying sections have a common anode and a separate first and second cathode, respectively.
A current-sensing circuit of the kind indicated above, and more especially the power semiconductor arrangement described in the preamble, are known from EP-A-O 139 998 which corresponds to U.S. Pat. No. 4,783,690 filed on Nov. 8, 1988.
In a practical embodiment the known power semiconductor arrangement contains a first current-carrying section with a large number of basic semiconductor elements, such as diodes, bipolar and/or field effect transistors and thyristors. The second current-carrying section has a significantly smaller number of such basic semiconductor elements or only one such basic semiconductor element. It is also possible for both the first and second current-carrying sections to contain only one basic semiconductor element, each of which however then has a different construction and/or geometry.
In a few power semiconductor arrangements provision may also be made for several second current-carrying sections.
In addition, control electrodes of the first and second current-carrying section may be connected to each other, either in the semiconductor body or externally.
In this known power semiconductor arrangement the current level in the second current-carrying section may be said to be proportional to the current level in the first current-carrying section, as a result of which the current level in the first current-carrying section can be sensed by an external low power circuit because only a fraction of the output current of the power semiconductor arrangement, i.e. the output current of the second current-carrying section, need be sensed in order to be able to determine the current level in the first current-carrying section.
It has been found, however, that under certain circumstances, for example a change in the input impedance of the current-sensing circuit and/or of the load connected to the semiconductor power arrangement, the output current of the semiconductor power arrangement at the first cathode and the measuring current at the second cathode are certainly not proportional to each other.